8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets, five torque-transmitting devices, one fixed interconnection, three external gear sets and a final drive gear set. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with one of the external gear sets. The five torque-transmitting devices provide interconnections between various planetary and external gear members, the input shaft, and the transmission housing, and are operated in combinations of three to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission in a front wheeldrive configuration having three planetary gear sets, three externalgear sets and a final drive gear set that are controlled by fivetorque-transmitting devices to provide eight forward speed ratios andone reverse speed ratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission in a front wheel drive configuration having three planetarygear sets, three external gear sets and a final drive gear setcontrolled to provide eight forward speed ratios and one reverse speedratio.

The transmission family of the present invention has three planetarygear sets positioned along first and second axes, wherein each planetarygear set includes a first, second and third member, which members maycomprise a sun gear, a ring gear, or a planet carrier assembly member,in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

An interconnecting member continuously connects the third member of thesecond planetary gear set with the second member of the third planetarygear set.

Three external gear sets are positioned for transferring torque betweenthe first and second axes, and each including first and secondintermeshed external gears. A final drive external gear set is connectedto an output member.

The input member is continuously connected with the second member of thefirst planetary gear set. The output member is continuously connectedwith the second external gear (driven gear) of the final drive externalgear set.

A first torque-transmitting device, such as a brake, selectivelyconnects the first member of the first planetary gear set with astationary member (transmission housing/casing).

A second torque-transmitting device, such as a clutch, selectivelyconnects the first external gear of the third external gear set with theinput member.

A third torque-transmitting device, such as a clutch, selectivelyconnects the second member of the second planetary gear set with thethird member of the third planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first external gear of the second external gear set withthe first external gear of the third external gear set.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the second external gear of the first external gear set withthe third member of the third planetary gear set.

The five torque-transmitting devices are selectively engageable incombinations of three to yield eight forward speed ratios and onereverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary and external gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The front wheel drive planetary transmission 14 includes an input member17 continuously connected with the engine 12, a planetary geararrangement 18, and an output member 19 continuously connected with thefinal drive mechanism 16. The planetary gear arrangement 18 includesthree planetary gear sets 20, 30, 40, three external gear sets, 50, 54,58 and a final drive gear set 62. The planetary and external gear sets20, 30, 40, 50, 54, and 58 are positioned along first and second axes91, 93 as shown.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the ring gear member 24 and the sun gear member 22.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the sun gear member 32 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and are disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The external gear set 50 includes first and second intermeshed externalgears 51 and 52. The external gear set 54 includes first and secondintermeshed external gears 55 and 56. The external gear set 58 includesfirst and second intermeshed external gears 59 and 60. The external gearsets 50, 54, 58 are positioned to transfer torque between the first andsecond axes 91, 93.

The final drive external gear set 62 includes the external drive gear 63and the external driven gear 64.

The planetary gear arrangement also includes five torque-transmittingdevices 80, 82, 83, 84 and 85. The torque-transmitting device 80 is astationary-type torque-transmitting device, commonly termed brake orreaction clutch. The torque-transmitting devices 82, 83, 84 and 85 arerotating-type torque-transmitting devices, commonly termed clutches.

The input member 17 is continuously connected with the planet carrierassembly member 26 of the planetary gear set 20. The output member 19 iscontinuously connected with the driven external gear 64 of the finaldrive external gear set 62.

An interconnecting member 70 continuously connects the ring gear member34 of the planetary gear set 30 with the planet carrier assembly member46 of the planetary gear set 40.

The sun gear member 22 of the planetary gear set 20 is continuouslyconnected with the first external gear 51 of the first external gear set50. The ring gear member 24 of the planetary gear set 20 is continuouslyconnected with the first external gear 55 of the second external gearset 54. The sun gear member 32 of the planetary gear set 30 iscontinuously connected with the second external gear 56 of the secondexternal gear set 54. The sun gear member 42 of the planetary gear set40 is continuously connected with the second external gear 60 of thethird external gear set 58. The planet carrier assembly member 46 of theplanetary gear set 40 is continuously connected with the external drivegear 63 of the final drive external gear set 62.

A first torque-transmitting device, such as brake 80, selectivelyconnects the sun gear member 22 of the planetary gear set 20 with thetransmission housing 90. A second torque-transmitting device, such asclutch 82, selectively connects the first external gear 59 of the thirdexternal gear set 58 with the input member 17. A thirdtorque-transmitting device, such as clutch 83, selectively connects theplanet carrier assembly member 36 of the planetary gear set 30 with thering gear member 44 of the planetary gear set 40. A fourthtorque-transmitting device, such as clutch 84, selectively connects thefirst external gear 55 of the second external gear set 54 with the firstexternal gear 59 of the third external gear set 58. A fifthtorque-transmitting device, such as clutch 85, selectively connects thesecond external gear 52 of the first external gear set 50 with the ringgear member 44 of the planetary gear set 40.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of three to provide eight forward speed ratios and onereverse speed ratio, all with single transition sequential shifts and adouble overdrive ratio.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.50, while the step ratio between the reversespeed ratio and first forward ratio is −0.27.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Vertical dashed lines with a grounded pivot point represent externalgear sets. Further explanation of the format, purpose and use of leverdiagrams can be found in SAE Paper 810102, authored by Benford, Howardand Leising, Maurice, “The Lever Analogy: A New Tool in TransmissionAnalysis”, 1981, which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive mechanism 16, a first planetary gear set 20A having threenodes: a first node 22A, a second node 26A and a third node 24A; asecond planetary gear set 30A having three nodes: a first node 32A, asecond node 36A and a third node 34A; and a third planetary gear set 40Ahaving three nodes: a first node 42A, a second node 46A and a third node44A. The powertrain 10 also includes a first external gear set 50Ahaving two external gears: a first external gear 51A and a secondexternal gear 52A; a second external gear set 54A having two externalgears: a first external gear 55A and a second external gear 56A; a thirdexternal gear set 58A having two external gears: a first external gear59A and a second external gear 60A; and a final drive gear set 62A withtwo external gears: a external drive gear 63A and a external driven gear64A.

The input member 17 is continuously connected with the node 26A. Theoutput member 19 is continuously connected with the external gear 64A.

The node 34A is continuously connected with the node 46A viainterconnecting member 70.

A first torque-transmitting device, such as brake 80, selectivelyconnects the node 22A with the transmission housing 90. A secondtorque-transmitting device, such as clutch 82, selectively connects theexternal gear 59A with the input member 17. A third torque-transmittingdevice, such as clutch 83, selectively connects the node 36A with thenode 44A. A fourth torque-transmitting device, such as clutch 84,selectively connects the external gear 55A with the external gear 59A. Afifth torque-transmitting device, such as clutch 85, selectivelyconnects the external gear 52A with the node 44A.

To establish ratios, three torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row of FIG. 1 b. For example, to establishreverse gear, the brake 80 and clutches 83, 85 are engaged. The brake 80engages the node 22A with the transmission housing 90. The clutch 83engages the node 36A with the node 44A. The clutch 85 engages theexternal gear 52A with the node 44A. Likewise, the eight forward ratiosare achieved through different combinations of clutch engagement as perFIG. 1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members, said gear sets being positioned along firstand second axes; an interconnecting member continuously connecting saidthird member of said second planetary gear set with said second memberof said third planetary gear set; three external gear sets positionedfor transferring torque between said first and second axes, said threeexternal gear sets each including first and second intermeshed externalgears; and five torque-transmitting devices for selectivelyinterconnecting said members of said planetary gear sets or said firstand second external gears of said three external gear sets with eachother, with a stationary member, with said input member, or with othermembers of said planetary gear sets, said five torque-transmittingdevices being engaged in combinations of three to establish at leasteight forward speed ratios and at least one reverse speed ratio betweensaid input member and said output member.
 2. The transmission of claim1, wherein a first of said five torque-transmitting devices is operablefor selectively connecting said first member of said first planetarygear set with said stationary member.
 3. The transmission of claim 2,wherein a second of said five torque-transmitting devices is operablefor selectively connecting said first external gear of said thirdexternal gear set with said input member.
 4. The transmission of claim3, wherein a third of said five torque-transmitting devices is operablefor selectively connecting said second member of said second planetarygear set with said third member of said third planetary gear set.
 5. Thetransmission of claim 4, wherein a fourth of said fivetorque-transmitting devices is operable for selectively connecting saidfirst external gear of said second external gear set with said firstexternal gear of said third external gear set.
 6. The transmission ofclaim 5, wherein a fifth of said five torque-transmitting devices isoperable for selectively connecting said second external gear of saidfirst external gear set with said third member of said third planetarygear set.
 7. The transmission defined in claim 1, wherein said firstmember of said first planetary gear set is continuously connected withsaid first external gear of said first external gear set; said thirdmember of said first planetary gear set is continuously connected withsaid first external gear of said second external gear set; said firstmember of said second planetary gear set is continuously connected withsaid second external gear of said second external gear set; said firstmember of said third planetary gear set is continuously connected withsaid second external gear of said third external gear set; and saidsecond member of said third planetary gear set is continuously connectedwith an external drive gear of a final drive external gear set.
 8. Thetransmission of claim 1, wherein said first, second and third members ofsaid first, second and third planetary gear sets comprise a sun gearmember, a planet carrier assembly member and a ring gear member,respectively.
 9. The transmission of claim 1, wherein said input memberis continuously connected with said second member of said firstplanetary gear set, and said output member is continuously connectedwith a driven external gear of a final drive external gear set.
 10. Amulti-speed transmission comprising: an input member; an output member;first, second and third planetary gear sets each having first, secondand third members, said planetary gear sets being positioned along firstand second axes; an interconnecting member continuously connecting saidthird member of said second planetary gear set with said second memberof said third planetary gear set; three external gears sets positionedfor transferring torque between said first and second axes, said threeexternal gear sets each including first and second intermeshed externalgears; a first torque-transmitting device selectively connecting saidfirst member of said first planetary gear set with a stationary member;a second torque-transmitting device selectively connecting said firstexternal gear of said third external gear set with said input member; athird torque-transmitting device selectively connecting second member ofsaid second planetary gear set with said third member of said thirdplanetary gear set; a fourth torque-transmitting device selectivelyconnecting said first external gear of said second external gear setwith said first external gear of said third external gear set; a fifthtorque-transmitting device selectively connecting said second externalgear of said first external gear set with said third member of saidthird planetary gear set; and said five torque-transmitting devicesbeing engaged in combinations of three to establish at least eightforward speed ratios and at least one reverse speed ratio between saidinput member and said output member.
 11. The transmission of claim 10,wherein said first, second and third members of said first, second andthird planetary gear sets comprise a sun gear member, a planet carrierassembly member and a ring gear member, respectively.
 12. Thetransmission of claim 10, wherein said first member of said firstplanetary gear set is continuously connected with said first externalgear of said first external gear set; said third member of said firstplanetary gear set is continuously connected with said first externalgear of said second external gear set; said first member of said secondplanetary gear set is continuously connected with said second externalgear of said second external gear set; said first member of said thirdplanetary gear set is continuously connected with said second externalgear of said third external gear set; and said second member of saidthird planetary gear set is continuously connected with an externaldrive gear of a final drive external set.
 13. The transmission of claim10, wherein said input member is continuously connected with said secondmember of said first planetary gear set, and said output member iscontinuously connected with a second external gear of a fourth externalgear set.
 14. A multi-speed transmission comprising: an input member; anoutput member; first, second and third planetary gear sets each having asun gear member, a planet carrier assembly member and a ring gearmember, said gear sets being positioned along first and second axes; aninterconnecting member continuously connecting said ring gear member ofsaid second planetary gear set with said planet carrier assembly memberof said third planetary gear set; three external gears sets positionedfor transferring torque between said first and second axes, said threeexternal gear sets each including first and second intermeshed externalgears; a first torque-transmitting device selectively connecting saidsun gear member of said first planetary gear set with a stationarymember; a second torque-transmitting device selectively connecting saidfirst external gear of said third external gear set with said inputmember; a third torque-transmitting device selectively connecting saidplanet carrier assembly member of said second planetary gear set withsaid ring gear member of said third planetary gear set; a fourthtorque-transmitting device selectively connecting said first externalgear of said second external gear set with said first external gear ofsaid third external gear set; a fifth torque-transmitting deviceselectively connecting said second external gear of said first externalgear set with said ring gear member of said third planetary gear set;and said five torque-transmitting devices being engaged in combinationsof three to establish at least eight forward speed ratios and at leastone reverse speed ratio between said input member and said outputmember.